The invention pertains to a screw compressor with the features indicated in the preamble of claim 1.
Screw compressors of this type are known from EP 0 993 553 B1 and EP 1 163 452 B1, for example. In these references, a vent channel that is open to the atmosphere is connected to the relief chamber of the sealing arrangement.
The present invention has particular advantages when applied to a screw compressor that compresses a gaseous medium such as air to very high pressures, for example in the range of 30 to 50 bar, and in particular where the application involves the high pressure stage of a two or three stage compressor system. The invention relates to such a multi-stage screw compressor system, in particular a three-stage screw compressor system.
Due to the high compression in the compressor, the sealing arrangements that seal the pressurized side of the rotor shafts in the rotor housing are subjected to a very high pressure load. Even if the sealing arrangement consists of a large number of sequentially arranged seal rings, the pressure drop across the entirety of the sealing arrangement is not even, but rather it occurs primarily at the seal rings located external to the rotor, i.e. the farthest ones from it. Consequently, they are subjected to a higher mechanical load.
The object of the invention is to construct the sealing arrangement on the pressurized side of the shaft of a screw compressor of the type indicated such that the pressure drop along the sealing arrangement can be controlled and smoothed out so that the reliability of the seal can be improved, especially for very high final pressures in the screw compressor.
The solution to this objective is indicated in claim 1. The dependent claims refer to further advantageous features of the invention.
According to the invention, it was found that by providing a defined intermediate pressure at a defined intermediate position in the sealing arrangements on the pressurized side of the rotor shafts, the pressure in the sealing arrangement drops in a controlled, even manner. The result is an especially effective and reliable seal, and the minimization of pressure losses as a result of gas leakage.